Varying-frequency system of radiosignaling



Nov. 8, 1927. 1,648,682

I J. H.' HAMMOND, JR

VARYING FREQUENCY SYSTEM OF RADIOSIGNALING Filed June 28. 1923 3 Sheets-Sheet l Hi6 A TTOR/VEY Nov. 8, 1927. 4 I 1,648,682

'- J. H. HAMMOND, JR

v VARYING FREQUENCY SYSTEM OF RADIOSIGNAPING Filed June 28. 1925 a sheetssheet 2 Nov. 8, 1927.- 1,648,682

J. H. HAMMO D.- .JR

VARYING FREQUENCY SYSTEM 'OF RADIQSI GNA LING" Filed June 28.. 1923 s Sheets-Sheet 5 IN VE N T05 Patented Nov. 8, 1927.

UNITED STATES JOHN HAYS HAMMOND, 53., 01?

GLOUCEETER, MASSACHUSETTS.

VARYING-FREQUENCY SYSTEM Q13 RADIOSIGNALING.

Application filed June 28,

Some of the objects of this invent-ion are to provide a system of radio signaling in which the carrier wave is periodically'varied in frequency, at a rate above audibility, and to provide other improvements as will appear hereinafter.

In the accompanying drawings Figs. 1, 2, 3 and 4 are diagrams of four difierent forms of transmitting systems constructed in accordance with this invention.

Since the transmitters diagrammed in Figs. 1 to 4 differ only as to means for varying the frequency of the carrier wave, and since the same generating and radiating system is used, the description of these given for Fig. 1 applies to transmitters shown in Figs.

'2, 3 and 4. Referring to Fig. 1, the radiating system of the transmitter here shown comprises antenna 10, connected to inductance 11, and to ground 12, through some device 13, which is so operated upon as to change the electrical period of the radiating system. In this case a condenser 13 is operated upon by an are 30.

For generating the carrier wave, a vacuum tube oscillator 16, whose filament is heated by battery 17, is connected to a coil 14 and a battery 15, so as to generate, in a well known manner, oscillations whose frequency is determined by the characteristics of the antenna system to which oscillator 16 is coupled by thecoils 14 and 11. Any other source of radio-frequent oscillations may be used instead of the vacuum tube oscillator 16, provided the frequency of the emitted waves is determined by the characteristics of the antenna system.

Referring now only to Fig. 1, the condenser 13 is connected across the terminals of the are 30, which is fed from a direct current source, through choke coils 34 and resistances 35. The are 30, being shunted by condensers 31 and 32 and an inductance 33, oscillates in a frequency which is determined by the inductance and capacityof said shunt circuit, and which can be easily varied by short-circuiting the condenser 32 by a key 36. The are frequency is adjusted by means of the condenser 31, to a value above audibility; say 21,000 cycles per second, with the key 36 open, and 20,000 cycles per second with the key 36 closed.

The effect of connecting an oscillating arc, such as described above, across the condenser 13, is that of shunting said condenser with a periodically varying resistance. The value 1923. Serial No. 648,299.

of this resistance may, periodically, become so low as to form practically a short circuit to the condenser 13. Whenever this condenser is short-circuited, there will be a change in the electrical-period of the antenna. system, and hence a corresponding change in the wave length of the carrier wave, say from 400 to 450 meters.

Therefore, from this transmitter there are radiated waves whose frequency is varied at a predetermined, superaudible rate, signaling being accomplished by slightly varying said rate by means of the key 36. An ordinary radio receiving station would be unable to intercept messages transmitted in this manner because it is necessary to successively tune to, and detect the carrier wave, tune to and detect the superimposed second ary frequency, and finally render the latter audible by hetrodyning or chopping.

In Fig. 2 is shown a transmitter differing from that in Fig. 1 only by a frequency varying device 113, consisting of.a magnetically controlled variable inductance, constructed in the following manner: A core 143, consisting of compressed iron filings, is wound with a radio-frequency winding 142, over which is placed a control winding 141. The latter is supplied with current from a battery 131 through choke coils 130 and a resistance 132. adjusted so that the magnetizing force of the control winding 141 is just sufficient to bring. the iron core to the knee of its magnetization curve. When so adjusted, the variable inductance device 113 is very sensitive to small variations in the control winding current, such as those impressed by an oscillating vacuum tube 133. This oscillating vacuum tube 133, whose filament is heated by battery 134, is connected through a plate battery-135 to a coil 136. Inductively coupled to said coil 136 is a coil 137 forming, with condensers 138 and. 139 and control winding 141, an oscillatory circuit energized by the oscillating vacuum tube 134 which generates oscillations in a well known manner. The frequency of these oscillations is determined by the inductance and capacity included in the circuit composed of the coil 137, control winding 141 and condensers 138 and 139. This frequency is adjusted by means .of the condenser 139 to a value above audibility, say 21,000 cycles per second, and by superimposing this frequency upon the magnetizing current from the battery 131, the magnetism of the core 14-3 will be altered once per oscillatory cycle or 21,000 times per second. As the flux in the iron core 143 varies, the effective inductance of the radioefrequent winding 142 will vary in a well known manner so that the ware length of the waves radiated from the antenna system will Vary at the super-audible rate, determined by the number of oscillations per second of the oscillator 133. This rate can be easily Varied by short-circuiting the condenser 138 by a key 1&0. Closing the key140 decre tSes the frequency from, say, 21,000 to 20,000 cycles per second. Signaling can, therefordibe'accomplished by the manipulation of the key 140,111 a manner similar to that disclosed in description of transmitter in Fig. 1 of this invention. 7 V p 3 illustrates another means used to vary the trequency of the waves emitted from an antenna system excited by .a genera tor Sll'Illlfll'ptO that described in connection with the foregoing figures. Here a portion of the antenna inductance 313 is acted upon inductively by a coil 31 i carrying oscillating current from an are 318 ted by direct current source (not shown) through resistances 320 and choke coils 319, and shunted by the os; .ciliatory circuit comprising condensers 316 and 317 and the coil 31d.

The are supplies, tothis shunt circuit, an oscillating current whose frequency-is adjusted byineans of condenser 317to a value of, .say, 10,5.00 cycles per second, so that at each alternation, the current flowing through the coil 314; will act upon coil 313, producing periodic variations in emitted wave length at the rate of 21,000 per second. The rate of variation of the radiated wave may be easily changed from 21,000 to 20,000 per second by closing a key 315 which is arnnged to shortcircuit condenser 316. Signaling is thus accomplished by changing the frequency of the oscillating arc circuit which acts to produce a change inthe radiated wave length. An oscillating vacuuintube may, of course,be substituted for the above described oscillating arc.

In Fig. 41 is diagrammed a transmitter differing from that shown in Fig. 1 inthat the antenna condenser 13 is here shunted by a plurality of vacuum tubes instead of an are. On the right of the diagra n is the vacuum tube e38, whose filament is heated by battery .4 16, and so connected to plate battery 337 and to a coil 435, shunted bycondensers 139 and 4:40, that it will generate oscillations in the coil 435 in a well known manner; said oscillations being impressed on cuit of the vacuum tubes 4533. The OSCllltlir ing circuit of vacuum tube oscillator 433 is tuned, by means of the condenser 4:39, to a super'audible frequency of, say, 21,000 cycles per second, said frequency being, decreased to 20,000 cycles by the closing of a key 436 whichshort-circuits condenser 4&0.

A. plate battery 4:31 and a choke coil 430 is connected in series with the plate-filament circuit ,of theyacuurn tubes 1-33 at the purpose or adjusting the internal resistance of said plate-filament path. The choke coil 1430 prevents the condenser 13 from being shortcii'cuited by the plate battery 4:31 whiclu-in series with said choke coil, is connected to the terminals of said condenser 13. the nfective resistance of the plate-filament path of the tubes4i33 is lowered each tinie by the grids are charged positively, the resistance of said tubes will periodically wiry at Since superaudible rate of 21,000 per second. As

is well known, the effective capacity of a condenserni ay be varied by shunting t wlt-h a res stance, thus the effective capacity of the condenser 13 is periodically varied in respouse to the variation of the internal resistance of the bank of vacuum tubes 433. As a result of the periodic variation in capacity of the condenser 13, the radiated wave length will be periodically varied.

ti onof the key 436 i which, as described above, yaries the frequency of oscillator 43.8. This produces, through the medium of the vacuum tube bank 433, a' corresponding change inthe rate of variation of the eniitted wave length. i i

Having thus described this invention 1 claini:

1. In a signaling system, the con'ibination with means for producing periodic impulses having frequency above audibility and means including an oscillatory; are for of June, A. 1)., 1923.

JOHN HAYS HAMMOND, JR.

Si nalin is accom alished b in'ani ula-- 

